Theoretical studies on reactions of late transition metal complexes and stabilities of osmabenzynes

Abstract

Theoretical studies on the reaction mechanisms of late transition metal complexes and the stabilities of osmabenzynes are reported in this thesis. Having a clear picture of these two chemical aspects is useful in the synthesis of new compounds for application. The selection of reaction pathways between the β-hydrogen elimination and σ-bond metathesis followed by reductive elimination for palladium and platinum alkoxide complexes containing bidentate ligands, L2MX(OCY2H) (L2 = CH2NCHCHNCH2 and PH2CH2CH2PH2; M = Pd and Pt; X = CH3,OCH3, NH2, OH, HCOO, C1 and Br; Y = H and F), has been investigated by density functional theory calculations at the level of B3LYP. The effects of cis-ligand X, bidentate ligand L2, transition metal M and substituents Y have been examined. Three cases can be classified for Pd complexes with different ligand X. For Pt analogue higher reaction barriers have been found. Complexes with phosphine bidentate ligands have lower reaction barriers when compared to their analogous Pd complexes containing amine bidentate ligands. Fluoride substituted alkoxy ligands decrease the β-hydrogen elimination pathways barriers. The reaction mechanism of the hydrogenation of norbornadiene (NBD) through the dihydrogen complex [Ru(H2)(NBD)(PCP)]+ has also been explored using density functional theory calculations at the B3LYP level. It has been found that the hydrogenation of the NBD ligand is a stepwise process. The concerted process, in which both hydrogen atoms of the H2 ligand transfer at the same time, is not possible. In addition, theoretical calculations at the B3LYP level of the density functional theory have been carried out to study the factors influencing the stabilities of osmabenzyne complexes. How the substituents on the ring carbons affect the stabilities and reactivities has been examined. Through the molecular orbital analyses, we found that the π orbitals in the six-membered ring, which are located in the HOMO-LUMO region, play important roles in the stabilities as well as the reactivities.

Date of Award	2002
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology